As technology has progressed, wood-type club heads have evolved from the relatively small persimmon-wood heads to the “oversized” metal club heads typically found in most modern drivers. Despite the changes in size and materials over the years, modern drivers have failed to overcome certain shortcomings historically associated with traditional wood-type clubs.
For a golfer to extract maximum performance from a golf club, a club head having a mass in the range of 180-250 g is generally provided. A certain portion of the club head's mass is reserved for components that provide structural support. The remaining mass, referred to as discretionary mass, may be strategically distributed within the club head to improve the head's inertial properties and to orient the CG in a desired location.
In conventional drivers, favorable placement of the CG and enhancement of the moments of inertia (MOI) are limited by the available amount of discretionary mass. Conventional methods of increasing the discretionary mass, e.g. thinning the club head walls and utilizing light-weight materials, have yielded relatively small gains in available discretionary mass. Conventional drivers have generally failed to realize CG locations and moments of inertia necessary to deliver improved performance due to limited amounts of attainable discretionary mass.
Generally, golfers have a natural tendency to strike the golf ball about the face center of the club head. The face center, in most drivers, is the point on the face where maximum energy transfer occurs at ball impact and is also known as the Coefficient of Restitution (COR) “hot spot”. Although ball impact at the COR “hot spot” yields added performance benefits in the form of increased distance, it does not necessarily produce the most accurate ball flight if the COR “hot spot” is not aligned with the impact point on the club face where no head rotation or gear effect occurs, also known as the “sweet spot”, which is the orthogonal projection of the club head's center of gravity (CG) onto the striking face of the head. In currently available club heads, the “sweet spot” is generally located above the COR “hot spot” due to the high location of the club head's center of gravity. This unfavorable CG orientation produces a club head where only one of these performance variables, i.e., distance associated with the COR “hot spot” or accuracy associated with the “sweet spot”, may be maximized during a single golf shot.
Furthermore, this high “sweet spot” location on the face produces a statistically unfavorable ball contact pattern that results in decreased directional shot consistency. The natural tendency of the golfer to strike the ball about the face center, on average, results in a larger than desired distance between the location of the ball at impact and the “sweet spot”. This increased distance exaggerates both the head rotation and gear effect of the club head, causing a loss of carry distance and accuracy.
Shot accuracy and distance are also affected by the depth of the CG relative to the club face. In modern drivers, the CG is typically positioned near the face. This shallow CG placement prevents the club head from dynamically flexing the shaft toward alignment with the CG to loft the head and to close the face at impact with the ball. Additionally, a shallow CG decreases the radius of rotation of the face on off-center hits, thus decreasing shot accuracy.